Victoria Azarenka was rushed to hospital by ambulance after collapsing on court in the searing heat at the US Open.

The No.10 seed from Belorussia slumped to the ground after only 34 minutes of her secondround match against Gisela Dulko. After receiving medical treatment under an umbrella, she was taken off the court in a wheelchair.

It was a scorching day where temperatures topped 100-degrees.

"It is something serious," said Dulko. "I hope she will feel better soon.

"I was playing well but after that I don't think about tennis - I am worried about my opponent.

"I am from Argentina and used to hot weather. But even the first day I was here I was feeling dizzy. It is hard to play in these conditions. It's tough."

Azarenka appeared to struggle as early as the third game when the trainer was called. She received treatment for an arm injury but also complained of blurred vision. While serving for the fourth time in the match, she collapsed on the baseline, leading to gasps from the crowd.

Tournament referee Brian Earley said: "This does not seem to be primarily a heat-related illness."